Microsoft has released SQL Server 2008 R2 Service Pack 2, which is Build 10.50.4000. It includes the fixes up through SQL Server 2008 Service Pack 1 CU5. If you have already installed SQL Server 2008 R2 SP1 CU6 or CU7, you will want to wait until Microsoft releases SQL Server 2008 R2 SP2 CU1 (which should be relatively soon if past history is any guide). The release notes are here. This Service Pack is only for SQL Server 2008 R2.

This build chart should make the relationship between the SP1 and SP2 branches more clear. Although I don’t have a link, Microsoft will typically retire the RTM branch when Service Pack 2 has been released. That means that if you are still on the RTM branch, you are going to want to get on a newer branch (preferably SP2) as soon as you can.